1. Field of the Invention
The invention relates to an ink jet printer employing heat melted ink and to an ink jet device of the ink jet printer.
2. Description of Related Art
An ink jet printer capable of printing an image, such as characters and figures on a recording medium, by employing heat melted ink which is a solid under a normal temperature and is melted by the application heat is well known. The ink jet printer comprises an ink jet device for jetting the melted heat melted ink, based on image data, toward the recording medium. Generally, in the ink jet device, the heat melted ink is heated by a single heating element or a plurality of heating elements which heat at the same temperature. In either case, the heat melted ink is heated so as to reach a predetermined temperature. Thus, the heat melted ink is melted by the heat element and becomes a liquid. At this time, the heat melted ink has a jettable low viscosity. In other words, the ink jet device keeps all stored ink in a melted condition at all times so as to be able to jet the ink at any time.
On the other hand, another ink jet device comprising a first and a second heat element is also well known. The first heat element melts the ink so that it becomes a liquid. At this time, the ink has a jettable low viscosity. The second heat element rapidly further heats the ink in order to give a heat energy to the ink. The heat energy is a jet power for the ink. According to the jet power, the ink is jetted. The ink jet device of this second type is disclosed in Japanese Laid-Open Patent Publication No. 62-135375.
However, in the above-mentioned ink jet device, the melted ink is stored in the ink jet device so as to maintain the jettable low viscosity for a long time. In other words, since the ink is kept at a high temperature, the ink is always kept in the melted condition. Therefore, the following problems result. When the ink is kept at a high temperature in order to be in the melted condition for a long time, the heat causes the ink composition to deteriorate. As a result, the characteristics of the ink, for example, the color and viscosity of the ink change as time passes. Therefore, when an image is formed using the deteriorated ink, the image does not have a good printing quality. Moreover, when the ink comprising pigment as a color material is kept at a high temperature in order remain in the melted condition for a long time, subsidence and aggregation of the pigment result. As a result, an ink jet part (jet nozzle) is clogged or the characteristics of the ink, for example, the color or viscosity of the ink, are changed or both.